File to array of strings (line by line)

Question

I have text file and I want to save each line to array of strings (global defined as fileA). All I know is that all rows in file are shorter then 101 characters. I made 3 functions:

char * lineToString(char * filename, int line) - return value of selected line
int getLineCount(char * filename) - return number of lines in file (counting form 1)
char * fileToArray(char * filename) - return array of strings

I think this functions work as they should, problem is somewhere in main(). I had printed sizeof(...) just for debugging. Also there is many warnings in my code, how can I fix them?

Thanks!

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int MAX_LINES = 1000;       //0 <= x && x < 1000
int MAX_ROW_LENGTH = 101;   //100 + 1 ('\0')
char * fileA = NULL;


char * lineToString(char * filename, int line){
    FILE * file = fopen(filename, "r");
    int currLine = 1;
    int currCol = 0;
    char currChar;
    char * string = (char *) malloc(sizeof(char)*MAX_ROW_LENGTH);
    string[0] = '\0';
    if(file != NULL && line >= 1){
        while((currChar = getc(file)) != EOF){
            if(currLine == line){
                if(currChar == '\n'){
                    string[currCol] = '\0';
                    break;
                }else{
                    string[currCol] = currChar;
                    currCol++;
                }
            }

            if(currChar == '\n') currLine++;
        }
        fclose(file);
    }
    return string;
}

int getLineCount(char * filename){
    FILE * file = fopen(filename, "r");
    int count = 0;
    char c;
    if(file != NULL){
        while((c = getc(file)) != EOF)
            if(c == '\n') count++;  
        fclose(file);
    }   
    return count;
}

char * fileToArray(char * filename){
    int i;
    int lineCount = getLineCount(filename);
    char array[lineCount][MAX_ROW_LENGTH];
    for(i = 1; i <= lineCount; i++){
        strcpy(array[i], lineToString(filename, i));
        //printf("%s\n", array[i]);
    }
    printf("%d\n",sizeof(array));
    return array;
}

int main(int argc, char **argv){

    fileA = (char *) malloc(sizeof(fileToArray(argv[1])));
    strcpy(fileA, fileToArray(argv[1]));
    printf("%d\n", (int) sizeof(fileA));
    int i;
    for(i = 0; i < (int) sizeof(fileA); i++){
        printf("%s\n", fileA[i]);
    }
    return 0;
}

Console:

matjazmav:~/FRI13_14/SE02/P2/DN/DN08$ gcc 63130148-08.c -o 63130148-08
63130148-08.c: In function ‘fileToArray’:
63130148-08.c:58:2: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘long unsigned int’ [-Wformat]
63130148-08.c:59:2: warning: return from incompatible pointer type [enabled by default]
63130148-08.c:59:2: warning: function returns address of local variable [enabled by default]
63130148-08.c: In function ‘main’:
63130148-08.c:69:3: warning: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘int’ [-Wformat]
matjazmav:~/FRI13_14/SE02/P2/DN/DN08$ ./63130148-08 input-1a input-1b
808
8
Segmentation fault (core dumped)

Search google for the message of each warning in turn (start at the top and recompile with each fix); these aren't particularly nasty, you'll find the answers quite easily, one-by-one. For the first warning: you have missed a header. — Dave
– Dave, Commented May 10, 2014 at 14:33

James R Matey · Accepted Answer · 2014-05-10 15:55:28Z

There are routines in the standard libraries that you should consider using.

I try to use functions in the standard libraries rather than writing my own equivalents unless absolutely necessary. The functions in the libraries are almost certainly better than anything I would write -- unless I was in the business of writing code for standard libraries.

I am a little rusty on C, my preferences today are C++ and C#. Sorry if there are some grammatical errors in the pseudo code below.

Opening and closing a file for each read of a line is very inefficient.

Here are some functions of interest

getline -- see How to explain the parameters of getline() in C -- is a workhorse for such tasks. It will automagically allocate just enough storage for a line.

rewind -- see http://www.tutorialspoint.com/c_standard_library/c_function_rewind.htm

feof -- detect end of file on a stream, see http://www.tutorialspoint.com/c_standard_library/c_function_feof.htm

Pseudo code -- not tested:

FILE fileHandle;
fileHandle = fopen(filename, "r");

if (! fileHandle) yourErrorExit();

// Count the lines -- there may be a system call that will do this more efficiently
int fileLengthInLines = 0;
char *lineBuffer = (char*)malloc(sizeOf(char) * maximumSizeOfLine]);
int bytesRead;

while (! feof(fileHandle)) {
int err;
err = getline(&lineBuffer, &bytesRead, filehandle) // ignore the string returned
if (!err) ; // process error appropriately
fileLengthInLines ++;  // this gives you your length of file in lines
}
free(lineBuffer); // we won't use it again

// allocate your array
char **stringArray;
stringArray = (char**) malloc(sizeof(char*)*fileLengthInLines);  

rewind(fileHandle); // get back to start of file

// Read lines and store
int lineNumber = 0;
char *getlineBuffer = NULL; // to force getline to allocate
int lineLength;
while (! feof(fileHandle)) {
   if (! (lineLength = getline(&getLineBuffer, 0, fileHandle))) ; // process error
   stringArray[lineNumber] = getLineBuffer;
   getLineBuffer = NULL; // to force getline to allocate on next iteration
   lineNumber++;

}

fclose(fileHandle);

// Check that all lines are processed -- compare fileLengthInLines with lineNumber
// Be sure to deallocate stringArray and its strings when you are done

Thanks for this useful answer. What header file includes getline() function? Thanks again!

R Sahu · Accepted Answer · 2014-05-11 05:54:57Z

One problem I see is that you need to move the line

        if(currChar == '\n') currLine++;

inside the while loop.

I see a few more problems that I will be able to describe when I am on a full fledged computer, not a tablet.

Update

You have

char * fileToArray(char * filename){
    int i;
    int lineCount = getLineCount(filename);
    char array[lineCount][MAX_ROW_LENGTH];
    for(i = 1; i <= lineCount; i++){
        strcpy(array[i], lineToString(filename, i));
        //printf("%s\n", array[i]);
    }
    printf("%zu\n",sizeof(array));
    return array;
}

Problems with this function:

The return value of char* is not compatible with the return statement return array;. array can be treated as char (*)[MAX_ROW_LENTH], but not char*.
Even if the return type and return statements were made to match, the main problem is that you are trying to return a pointer to an object that will be deleted when the function returns. The pointer will be invalid in the calling function.

The line

    strcpy(array[i], lineToString(filename, i));

should be

    strcpy(array[i-1], lineToString(filename, i));

since array indexing in C starts with 0, not 1.

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